This invention relates to the use of an irreversible inhibitor of GABA-transaminase for the treatment of substance addiction and modification of behavior associated with substance addiction. Substance addiction, such as drug abuse, and the resulting addiction-related behavior are enormous social and economic problems that continue to grow with devastating consequences.
Substance addiction can occur by use of legal and illegal substances. Nicotine, cocaine, amphetamine, methamphetamine, ethanol, heroin, morphine and other addictive substances are readily available and routinely used by large segments of the United States population.
Many drugs of abuse are naturally occurring. For example, cocaine is a naturally occurring nonamphetamine stimulant derived from the leaves of the coca plant, Erythroylon coca. Coca leaves contain only about one-half of one percent pure cocaine alkaloid. When chewed, only relatively modest amounts of cocaine are liberated, and gastrointestinal absorption is slow. Certainly, this explains why the practice of chewing coca leaves has never been a public health problem in Latin America. The situation changes sharply with the abuse of the alkaloid itself.
It has been found that addicting drugs such as nicotine, cocaine, amphetamine, methamphetamine, ethanol, heroin, and morphine enhance (in some cases directly, in other cases indirectly or even trans-synaptically) dopamine (DA) within the mesotelencephalic reward/reinforcement circuitry of the forebrain, presumably producing the enhanced brain reward that constitutes the drug user""s xe2x80x9chigh.xe2x80x9d Alterations in the function of these DA systems have also been implicated in drug craving and in relapse to the drug-taking habit in recovering addicts. For example, cocaine acts on these DA systems by binding to the dopamine transporter (DAT) and preventing DA reuptake into the presynaptic terminal.
There is considerable evidence that nicotine, cocaine, amphetamine, methamphetamine, ethanol, heroin, morphine and other abused drugs"" addictive liability is linked to reuptake blockade in central nervous system (CNS) reward/reinforcement pathways. For example, cocaine-induced increases in extracellular DA have been linked to its rewarding and craving effects in rodents. In humans, the pharmacokinetics binding profile of 11C-cocaine indicates that the uptake of labeled cocaine is directly correlated with the self-reported xe2x80x9chighxe2x80x9d. In addition, human cocaine addicts exposed to cocaine-associated environmental cues experienced increased cocaine craving which is antagonized by the DA receptor antagonist haloperidol. Based upon the presumptive link between cocaine""s addictive liability and the DA reward/reinforcement circuitry of the forebrain, many pharmacologic strategies for treating cocaine addiction have been proposed.
In the past, one treatment strategy was to target directly the DAT with a high-affinity cocaine analog, thereby blocking cocaine""s binding. Another treatment strategy was to modulate synaptic DA directly by the use of DA agonists or antagonists. Yet another treatment strategy was to modulate synaptic DA, indirectly or trans-synaptically, by specifically targeting a functionally-linked but biochemically different neurotransmitter system.
A number of drugs have been suggested for use in weaning cocaine users from their dependency. Certain therapeutic agents were favored by the xe2x80x9cdopamine depletion hypothesis.xe2x80x9d It is well established that cocaine blocks dopamine reuptake, acutely increasing synaptic dopamine concentrations. However, in the presence of cocaine, synaptic dopamine is metabolized as 3-methoxytyramine and excreted. The synaptic loss of dopamine places demands on the body for increased dopamine synthesis, as evidenced by the increase in tyrosine hydroxylase activity after cocaine administration. When the precursor supplies are exhausted, a dopamine deficiency develops. This hypothesis led to the testing of bromocriptine, a dopamine receptor agonist. Another approach was the administration of amantadine, a dopamine releaser. Yet another approach, also based on the dopamine depletion hypothesis, was to provide a precursor for dopamine, such as L-dopa.
Agonists are not preferred therapeutic agents. A given agonist may act on several receptors, or similar receptors on different cells, not just on the particular receptor or cell one desires to stimulate. As tolerance to a drug develops (through changes in the number of receptors and their affinity for the drug), tolerance to the agonist may likewise develop. A particular problem with the agonist bromocriptine, for example, is that it may itself create a drug dependency. Thus, treatment strategies used in the past did not relieve the patient""s craving for cocaine. Moreover, by using certain agonists such as bromocriptine, a patient was likely to replace one craving for another.
Another drug that is frequently abused is nicotine. The alkaloid (xe2x88x92)-nicotine is present in cigarettes and other tobacco products that are smoked or chewed. It has been found that nicotine contributes to various diseases, including cancer, heart disease, respiratory disease and other conditions, for which tobacco use is a risk factor, particularly heart disease.
Vigorous campaigns against the use of tobacco or nicotine have taken place, and it is now common knowledge that the cessation of tobacco use brings with it numerous unpleasant withdrawal symptoms, which include irritability, anxiety, restlessness, lack of concentration, lightheadedness, insomnia, tremor, increased hunger and weight gain, and, of course, an intense craving for tobacco.
The addictive liability of nicotine has been linked to the rewarding/reinforcing actions and its effects on DA neurons in the reward pathways of the brain (Nisell et al., 1995; Pontieri, et al., 1996). For example, the acute systemic administration of nicotine, as well as numerous other drugs of abuse, produces an increase in extracellular DA levels in the nucleus accumbens (NACC), an important component of the reward system (Damsma et al., 1989; Di Chiara and Imperato, 1988; Imperato et al., 1986; Nisell et al., 1994a, 1995; Pontieri et al., 1996). Similarly, the infusion of nicotine into the ventral segmental area (VTA) of the rodent produces a significant increase in DA levels in the NACC (Nisell et al., 1994b).
A few pharmaceutical agents have been reported as useful to treat nicotine dependence, including nicotine substitution therapy such as nicotine gum, transdermal nicotine patches, nasal sprays, nicotine inhalers and bupropion, the first nonnicotinic treatment for smoking cessation (Henningfield, 1995; Hurt, et al., 1997).
Unfortunately, nicotine substitution therapy involves the administration of the nicotine which frequently leads to nicotine withdrawal and subsequent relapse to use of tobacco products. Thus, there is a need for a therapy having a desirable side effect profile, to relieve nicotine withdrawal symptoms, including the long term cravings for nicotine.
Other well known addictive substances are narcotic analgesics such as morphine, heroin and other opioids both natural and semisynthetic. Abuse of opioids induce tolerance and dependence. Withdrawal symptoms from the cessation of opioids use vary greatly in intensity depending on numerous factors including the dose of the opioid used, the degree to which the opioid effects on the CNS are continuously exerted, the duration of chronic use, and the rate at which the opioid is removed from the receptors. These withdrawal symptoms include craving, anxiety, dysphoria, yawning, perspiration, lacrimation, rhinorrhoea, restless and broken sleep, irritability, dilated pupils, aching of bones, back and muscles, piloerection, hot and cold flashes, nausea, vomiting, diarrhea, weight loss, fever, increased blood pressure, pulse and respiratory rate, twitching of muscles and kicking movements of the lower extremities.
Medical complications associated with injection of opioids include a variety of pathological changes in the CNS including degenerative changes in globus pallidus, necrosis of spinal gray matter, transverse myelitis, amblyopia, plexitis, peripheral neuropathy, Parkinsonian syndromes, intellectual impairment, personality changes, and pathological changes in muscles and peripheral nerves. Infections of skin and systemic organs are also quite common including staphylococcal pneumonitis, tuberculosis, endocarditis, septicemia, viral hepatitis, human immunodeficiency virus (HIV), malaria, tetanus and osteomyelitis. The life expectancy of opioid addicts is markedly reduced, due to overdose, drug-related infections, suicide and homicide.
Pharmaceutical agents used in treating opioid dependence include methadone, which is an opioid, and opioid antagonists, primarily naloxone and naltrexone. Clonidine has been shown to suppress some elements of opioid withdrawal but suffers from the side effects of hypotension and sedation, which can be quite extreme. Behavior-modifying psychological treatment and training are frequently adjunctive therapy used in association with pharmaceutical agents. There is a need for a therapy having a more desirable side effect profile, to relieve opioid addiction and withdrawal symptoms.
Ethanol is probably the most frequently used and abused depressant in most cultures and a major cause of morbidity and mortality. Repeated intake of large amounts of ethanol can affect nearly every organ system in the body, particularly the gastrointestinal tract, cardiovascular system, and the central and peripheral nervous systems. Gastrointestinal effects include gastritis, stomach ulcers, duodenal ulcers, liver cirrhosis, and pancreatitis. Further, there is an increased rate of cancer of the esophagus, stomach and other parts of the gastrointestinal tract. Cardiovascular effects include hypertension, cardiomyopathy and other myopathies, significantly elevated levels of triglycerides and low-density lipoprotein cholesterol. These cardiovascular effects contribute to a marked increase risk of heart disease. Peripheral neuropathy may be present as evidenced by muscular weakness, parathesias, and decreased peripheral sensation. Central nervous system effects include cognitive deficits, severe memory impairment degenerative changes in the cerebellum, and ethanol-induced persisting amnesiac disorder in which the ability to encode new memory is severely impaired. Generally, these effects are related to vitamin deficiencies, particularly the B vitamins.
Individuals with ethanol dependence or addiction exhibit symptoms and physical changes including dyspepsia, nausea, bloating, esophageal varices, hemorrhoids, tremor, unsteady gait, insomnia, erectile dysfunction, decreased testicular size, feminizing effects associated with reduced testosterone levels, spontaneous abortion, and fetal alcohol syndrome. Symptoms associated with ethanol cessation or withdrawal include nausea, vomiting, gastritis, hematemises, dry mouth, puffy blotchy complexion, and peripheral edema.
The generally accepted treatment of ethanol addiction and withdrawal is accomplished by administering a mild tranquilizer such a chlordiazepoxide. Typically, vitamins, particularly the B vitamins, are also administered. Optionally, magnesium sulfate and/or glucose are also administered. Nausea, vomiting and diarrhea are treated symptomatically at the discretion of the attending physician. Disulfiram may also be administered for help in maintaining abstinence. If ethanol is consumed while on disulfiram, acetaldehyde accumulates producing nausea and hypotension. There is a need for a therapy having a more desirable side effect profile, to relieve ethanol addiction and withdrawal symptoms.
Accordingly, there is still a need in the treatment of addiction to drugs of abuse to provide new methods which can relieve a patient""s craving by changing the pharmacological actions of drugs of abuse in the central nervous system.
The present invention, which addresses the needs of the prior art, provides methods for treating substance addiction and changing addiction-related behavior of a mammal, for example a primate, suffering from substance addiction by administering to the mammal an effective amount of a pharmaceutical composition including gamma vinylGABA (GVG). The amount of GVG varies from about 15 mg/kg to about 2 gm/kg, preferably from about 100 mg/kg to about 600 mg/kg, and most preferably from about 150 mg/kg to about 300 mg/kg.
In a preferred embodiment, the present invention provides a method of eliminating the effects of nicotine addiction by treating a mammal with an effective amount of a composition including GVG. When treating the effects of nicotine addiction the amount of GVG present in the pharmaceutical composition is from about 15 mg/kg to about 2 g/kg. Preferably, 75 mg/kg to about 150 mg/kg, and most preferably from about 18 mg/kg to about 20 mg/kg.
In yet another embodiment, the present invention provides a method for changing addiction-related behavior of a mammal suffering from addiction to drugs of abuse which comprises administering to the mammal an effective amount of gamma vinylGABA (GVG) or a pharmaceutically acceptable salt thereof, wherein the effective amount attenuates the rewarding/incentive effects of drugs of abuse selected from the group consisting of psychostimulants, narcotic analgesics, alcohols, nicotine and combinations thereof in the absence of altering rewarding/incentive effects of food in said mammal.
The amount of GVG varies from about 15 mg/kg to about 2 gm/kg, preferably from about 15 mg/kg to about 600 mg/kg, and most preferably from about 150 mg to about 600 mg/kg.
As a result of the present invention, methods of reducing substance addiction and changing addiction-related behavior are provided which are based on a pharmaceutical composition which is not itself addictive, yet is highly effective in ameliorating the addiction and the addictive behavior of addicted patients. The pharmaceutical composition useful for the method of the present invention inhibits or eliminates craving experienced by drug addicts for use of the drug of abuse. Moreover, the elimination of behavior associated with drugs of abuse occurs in the absence of an aversive or appetitive response to GVG. Moreover, behavior characteristics associated with dependency on drugs of abuse are reduced or eliminated in the absence of an alteration in the locomotor function of the primate.
In yet another embodiment, the invention includes a method for changing addiction-related behavior of a mammal suffering from addiction to drugs of abuse which comprises administering to the mammal an effective amount of gamma vinylGABA (GVG) or a pharmaceutically acceptable salt thereof, or an enantiomer or a racemic mixture thereof, wherein the effective amount is sufficient to diminish, inhibit or eliminate behavior associated with craving or use of drugs of abuse.
In another exemplary embodiment of the present invention, the method includes changing addiction-related behavior of a mammal suffering from addiction to drugs of abuse which comprises administering to the mammal an effective amount of a composition that increases central nervous system GABA levels wherein the effective amount is sufficient to diminish, inhibit or eliminate behavior associated with craving or use of drugs of abuse.
Other improvements which the present invention provides over the prior art will be identified as a result of the following description which sets forth the preferred embodiments of the present invention. The description is not in any way intended to limit the scope of the present invention, but rather only to provide a working example of the present preferred embodiments. The scope of the present invention will be pointed out in the appended claims.